Mineralization in calcified plaque is like that of cortical bone—Further evidence from ultrashort echo time (UTE) magnetic resonance imaging of carotid plaque calcification and cortical bone

Abstract

This study aims to investigate carotid plaque calcification (CPC) using two-dimensional (2D) and 3D ultrashort echo time (UTE) magnetic resonance imaging (MRI) sequences and compare T1, T2*, water concentration, and bone mineral density (BMD) of CPC with those of cortical bone. Twelve carotid plaque specimens and eight tibial cortical bone samples were imaged with UTE sequences. Adiabatic inversion recovery prepared UTE (IR-UTE) acquisitions were used for T2* measurement. Saturation recovery prepared UTE acquisitions were used for T1 measurement. Water concentration was measured by comparing signal from CPC and bone with that from a phantom. BMD was measured with μCT. Conventional gradient echo and fast spin echo images were also acquired for comparison. Our studies show that CPC and cortical bone have similar T1 and BMD values but different T2* and water concentration. For CPC T2*s ranged from 0.31 to 3.87 ms, T1s ranged from 114 to 332 ms, water concentrations ranged from 6.4% to 17.6%, and BMD ranged from 977 to 1319 mg/ml. For cortical bone T2*s ranged from 0.33 to 0.45 ms, T1s ranged from 198 to 254 ms, water concentrations ranged from 24.7% to 33.8%, and mineral densities ranged from 970 to 1287 mg/ml. On average CPC shows about 5% longer T1, 5% lower BMD, 440% longer T2*, and 130% lower water concentration when compared to human cortical bone. CPC bears remarkable similarities with cortical bone in terms of BMD and T1. CPC shows a higher mean T2* and a lower mean water concentration.